This invention relates to an integrated circuit (IC) analog-signal manipulating circuit (ASMC) having a frequency dependant transfer function wherein parameters that establish the frequency response of the transfer function are each attributable to the product of a resistance and a capacitance of the circuit, and more particularly pertains to such an ASMC wherein each of the frequency determining capacitors or resistors is a digitally programmable component that may be adjusted by a microprocessor to stabilize the corresponding RC product against changes with temperature.
A simple example of a digitally programmable analog-signal manipulating circuit is an integrator employing an integrator resistor and an integrator capacitor, wherein the transfer function of the integrator, with the Laplace frequency variable S, is 1/RCS.
Both the resistance R and the capacitance C change value as a function of temperature in a manner and to a degree depending mainly upon the materials of which the corresponding resistor body and capacitor dielectric are made. Thus, even with the most temperature stable resistors and capacitors the change in an RC product with temperature causes in many analog circuits an unwelcome change in the frequency response.
Furthermore, it is often difficult or impossible to build circuits with RC products that have a suitably predictable value or even a predictable temperature coefficient of RC product, especially for meeting specifications for stable circuit frequency responses over a broad range of operating temperatures.
It is therefore an object of this invention to provide an integrated analog signal manipulating circuit controllable by a microprocessor to have a temperature stable frequency response.
It is a further object of this invention to provide such a controllable integrated analog signal manipulating circuit that in effect has a uniformly predictable frequency response from chip to chip in spite of inevitable chip to chip RC-product differences.